In the fabrication of integrated devices, diverse materials are of interest, e.g., glasses, semiconductors, and electro-optic, magneto-optic, and acousto-optic crystals. Materials are chosen on the basis of desired optical and/or electrical properties, e.g., low insertion loss, high electro- or magneto-optical coefficient, and suitable bandgap, and with cost and ease of fabrication in mind. For example, silica-based glasses and lithium niobate crystals are suitable for the fabrication of inexpensive waveguides having low insertion loss, lithium niobate further having high electro-optic coefficients, and thus allowing highly efficacious modulation of the phase, polarization, and amplitude of guided light. Semiconductors offer the opportunity to vary the concentration of highly mobile carriers through doping and "band-gap engineering", allowing the fabrication of waveguides, sources, detectors, and high-speed electronics.
For optical sources such as light-emitting diodes and lasers, for photodetectors, and for optical amplifiers, Group III-V compound semiconductors have become materials of choice--to be combined, e.g., with glass waveguides in opto-electronic integrated circuits (OEIC's). Integration poses difficulties, however, in that customary methods of integrated device fabrication do not allow growth of single-crystal compound-semiconductor layers on substrates having random or incompatible surface structure. As a result, progress towards the commercialization of integrated optics has been impeded, recourse seeming necessary to the exclusive use of sub-optimal, crystallographically compatible materials, or else to the inclusion of discrete devices delicately aligned with substrate-supported waveguides ("flip-chip" technique).
Relevant with respect to the invention described below is the recent development of a so-called epitaxial lift-off technique, involving epitaxial growth of a film of a desired material on a first, auxiliary or growth substrate, followed by detaching and removal of the grown film for attachment or grafting onto a second, desired substrate. Processing of this type has received attention, e.g., as an alternative to lattice-mismatched epitaxial growth of gallium arsenide on silicon; specifically, as disclosed by E. Yablonovitch et al., "Extreme Selectivity in the Lift-off of Epitaxial GaAs Films", Applied Physics Letters 51 (1987), pp. 2222-2224, a gallium arsenide film can be grown on an intermediate aluminum arsenide layer on a gallium arsenide substrate, and the grown gallium arsenide film can be lifted off upon undercut etching--i.e., upon chemical dissolution of the intermediate layer. For further details and preferred embodiments of epitaxial lift-off processing see U.S. Pat. Nos. 4,846,931 and 4,883,561, issued to T. J. Gmitter et al. on Jul. 11, 1989 and Nov. 28, 1989, respectively; for exemplary uses of resulting films as bonded to desired substrates see, e.g., E. Yablonovitch et al., "Regrowth of GaAs Quantum Wells on GaAs Liftoff Films `Van der Waals Bonded` to Silicon Substrates", Electronics Letters, Vol. 25 (1989), p. 171; and E. Yablonovitch et al., "Double Heterostructure GaAs/AlGaAs Thin Film Diode Lasers on Glass Substrates", IEEE Photonics Technology Letters, Vol. 1 (1989), pp. 41-42.